According to the FDA's letter that was released by Pfizer on Wednesday, the delays in reporting side effects date back as far as 2004 and have grown in recent years.

Ronald Pace, director of FDA's New York office, told Pfizer that it had not properly documented or investigated reported problems in patients after the drugs were approved for use.

"FDA expects drug manufacturers to establish and implement reasonable mechanisms to assure that all serious and unexpected experiences are promptly recorded and investigated," Pace wrote.

Pace asked Kindler to arrange a meeting between the company and the agency over the violations. Pfizer said it received the letter on June 3.

The FDA conducted a 6-week inspection of Pfizer's New York headquarters in July and August of 2009. This is where agency inspectors found system-wide lapses at the world's largest drugmaker.

Pace wrote that the patient reports "contained serious and unexpected adverse events... that were not submitted until they were identified during the FDA inspection." Efforts to fix the problem "have been shown to be ineffective," he added.

Pfizer said in its statement that it would work with the FDA to satisfy the agency "and to assure optimal surveillance and reporting of post-marketing adverse events."

However, it also said that such individual reports are just one part of its overall monitoring of the drugs it sells and that it "believes we provide complete and accurate data to determine the benefit and risk profile for all of our medicines, and to enable their safe and appropriate use."

And with Pfizer's Bextra painkiller, which is now withdrawn, FDA granted the company a waiver to allow 60 days to forward any complaints, a window of time the drugmaker still missed.

According to the FDA, Pfizer initially blamed the problems on a new computerized system to handle the reports. Pfizer said the staff was also not properly trained.

Pfizer told the FDA in September in 2009 that it would update user manuals, better train its staff in the computerized reporting system and take other action.

Despite those steps, the FDA still said that the company's actions were "inadequate."

The FDA said that Pfizer told the agency that its reporting improved after May 2009, but did not include any data backing up that claim. The company did not prove to the FDA that it trained all the employees it said it would.

The FDA said in its letter that Pfizer's delays in telling the agency about reported complaints have only grown. The letter said about 4 percent of Pfizer's 80,560 reports were sent late from March 2006 through December 2008, compared with 9 percent from December 2008 to June 2009.

The FDA also cited Pfizer for not immediately telling the FDA about thefts and significant losses of its medications.

Pace requested an immediate meeting and asked for the problems to be fixed with 15 days, or an explanation provided if it would take longer. He also called for Pfizer to submit a revised plan to fix the problems.

Pace said in the letter that failure to fix the problems could result in legal action without notice and the FDA could delay action in approving the company's pending drugs, among other penalties.